[SYCL][NFC] Small refactoring

[romanovvlad]

1. Use C++ cast instead of C casts
2. Move implemenetation of several handler methods to source dir

[v-klochkov]

Looks good, but accessor.cpp LIT test reported a fail and it is known as a stable test.

[romanovvlad]

Looks good, but accessor.cpp LIT test reported a fail and it is known as a stable test.

It's not old one accessor from basic_tests, this one from atomic_ref and has been added quite recently.
I have seen this fail in another PR, so it's not related to the change.
Trying to root cause the fail, but it turns to be difficult one.

[romanovvlad]

Looks good, but accessor.cpp LIT test reported a fail and it is known as a stable test.

It's not old one accessor from basic_tests, this one from atomic_ref and has been added quite recently.
I have seen this fail in another PR, so it's not related to the change.
Trying to root cause the fail, but it turns to be difficult one.

atomic_ref/accessor should start passing after recent update of L0.